COLUMBIA BANKING SYSTEM, INC.

Refer to "Part I—Item 1A—Risk Factors" in our Annual Report on Form 10-K for the year ended December 31, 2024 for a discussion of risk factors relating to the Company's business. These factors could materially and adversely affect our business, financial condition, liquidity, results of operations and capital position, and could cause our actual results to differ materially from our historical results or the results contemplated by the forward-looking statements contained in this Quarterly Report on Form 10-Q. The Company believes that there has been no material change in its risk factors as previously disclosed in the Company's Form 10-K for the year ended December 31, 2024 other than as set forth below.

Combining Columbia and Pacific Premier may be more difficult, costly or time-consuming than expected, and Columbia may fail to realize the anticipated benefits of the acquisition of Pacific Premier.

Prior to the closing of the acquisition of Pacific Premier on August 31, 2025, Columbia and Pacific Premier operated independently. The success of the acquisition, including anticipated benefits and cost savings, will depend, in part, on our ability to successfully integrate Pacific Premier's business into Columbia's in a manner that permits growth opportunities and does not materially disrupt the existing customer relations nor result in decreased revenues due to loss of customers. It is possible that the integration process could result in the loss of key employees, the disruption of Columbia's ongoing businesses or inconsistencies in standards, controls, procedures, and policies that adversely affect Columbia's ability to maintain relationships with clients, customers, depositors, and employees or to achieve the anticipated benefits and cost savings of the acquisition. The loss of key employees could adversely affect Columbia’s ability to successfully conduct its business, which could have an adverse effect on Columbia’s financial results and the value of its common stock. If Columbia experiences difficulties with the integration process, the anticipated benefits of the acquisition may not be realized fully or at all, or may take longer to realize than expected. As with any acquisition involving financial institutions, there also may be business disruptions that cause Columbia to lose customers or cause customers to remove their accounts from Columbia and move their business to competing financial institutions. Integration efforts will also divert management attention and resources. These integration matters could have an adverse effect on Columbia for an undetermined period after completion of the acquisition. In addition, the actual cost savings of the acquisition could be less than anticipated.

Columbia may be unable to retain Columbia and/or legacy Pacific Premier personnel successfully.

The success of the acquisition of Pacific Premier will depend in part on Columbia's ability to retain the talent and dedication of key employees. It is possible that these employees may decide not to remain with Columbia following the consummation of the acquisition. If Columbia is unable to retain key employees, including management, who are critical to the successful integration of Pacific Premier's business and the future operations of Columbia, Columbia could face disruptions in its operations, loss of existing customers, loss of key information, expertise, or know-how and unanticipated additional recruitment costs. In addition, following the acquisition, if key employees terminate their employment, Columbia's business activities may be adversely affected, and management's attention may be diverted from successfully hiring suitable replacements, all of which may cause the Columbia's business to suffer. Columbia also may not be able to locate or retain suitable replacements for any key employees who leave Columbia.